Thermal printer



May 5, 1970 c. R. LOUGHRY ETAL 3,509,980

THERMAL PRINTER Filed March 12, 1968 4 Sheets-Sheet 1 t FIG. I

INVENTORS CLARK R. LOUGHRY & RICHARD D. JOYCE BY WaKA THEIR ATTORNE S May 5, 1970 c. R. LOUGHRY ETAL 9,

THERMAL PRINTER Filed March 12, 1968 4 Sheets-Sheet 2 INVENTORS CLARK R. LOUGHRY & RICHARD D. JOYCE THEIR ATTORN (S LINE FEED SOLENOID oNE SHOT SOLENOID RETURN 228 RETURN MOTOR J FLIP-FLOP SIGNAL TRANSD. i

RETURN ONE-SHOT f 244 76 ADVANCE ONE-SHOT y 1970 c. R. LOUGHRY ETAL 3,509,980

THERMAL PRINTER Filed March 12, 1968 4 Sheets-Sheet 3 FIG 6 66 INVENTORS CLARK R. LOUGHRY 8 I20 I66 92% I683] THEIR ATTORNEYS May 5, 1970 c. R. LOUGHRY EFAI- 3,509,930

THERMAL PRINTER Filed March 12, 1968 4 Sheets-Sheet 4 INVENTORS CLARK R. LOUGHRY 8| RICHARD D. 1%

THEIR ATTORNEYS United States Patent 3,509,980 THERMAL PRINTER Clark R. Loughry and Richard D. Joyce, Kettering, Ohio,

assignors to The National Cash Register Company,

Dayton, Ohio, a corporation of Maryland Filed Mar. 12, 1968, Ser. No. 712,545 Int. Cl. GOld 15/10 US. Cl. 197--1 7 Claims ABSTRACT OF THE DISCLOSURE A compact thermal printer which operates on a low power input. A matrix-type print head is indexed along a print line in the printer by an endless belt, and the print head is slidably mounted on a guide bar member which pivots to force the print head into engagement with a thermally sensitive print medium located at the print line. After printing, the guide bar member pivots the head away from the print medium, and the print head is indexed to the next printing position to permit immediate viewing of the character printed. Transport means, including ratchet and pawl members, solenoid members, and an electric motor, utilize a small power input to index the print head and return it to the starting point at the print line.

The invention described herein was developed in the course of performing a contract With the United States Department of the Army.

BACKGROUND OF THE INVENTION This invention relates to a compact thermal printer which utilizes a matrix-type print head and a thermally sensitive print medium.

The prior-art thermal printers have been made only with stationary print heads requiring that the print medium be moved relative to the head. These printers were bulky and expensive to produce, and required a large power input to operate them. In addition, alignment, evenness of pressure, and abrasion problems existed between the heads and the print medium. To produce a compact thermal printer, in view of these problems, seemed to be a formidable task.

An experimental study was conducted to develop and demonstrate the feasibility of a miniaturized thermal printer which utilized a matrix-type print head. The following guidelines were used as objectives in the development phase: (1) low power carriage movement which permits the carriage to return to starting print position in one printing interval; (2) immediate visibility of the last character printed; (3) a master copy and a first copy made within the machine; (4) three or more subsequent copies made externally of the printer While using only pressure rollers; and (5) the use of a suitable thermal sensitive paper to meet the requirement of objectives (3) and (4). These last three objectives are not a part of this ap plication.

SUMMARY The printer apparatus of this invention includes a frame means having a print line located therein, said print line having a plurality of print positions located therealong. A guide bar means is pivotally mounted in said frame means for movement between non-printing and printing positions relative to said print line. A thermal, matrix-type print head is slidably mounted on said guide bar means for movement between the first and last print positions along said print line. When the guide bar means is in the non-printing position, the print head is out of engagement with a thermally sensitive print medium positioned at the print line, and when the guide bar means is rotated to the printing position, the print head carried thereby is forced into engagement with the print medium to elIect the printing thereon. Transport means are provided for rotating the guide bar means between the nonprinting position and the printing position, and for sliding the print head along the guide bar means to index it one print position at a time towards the last print position. When the print head reaches the last print position, return means are activated to automatically return the print head to the first print position, and feed means are activated to advance the print medium one line.

United States Patent No. 3,139,026, issued June 30, 1964, on the application of Robert C. Meckstroth et al., shows a thermal printer which utilizes a stationary matrixtype print head. Details of the print head are also shown in United States Patent No. 3,161,457, which issued Dec. 15, 1964, on the application of Hans Schroeder et al.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view of the top of the printer apparatus of this invention showing the general arrangement of the print line, the print head, the guide bar means on which the head is slidably mounted, means for returning the print head to a first print position, and the means for feeding the print medium past the print line.

FIG. 2 is a side elevational view, partly in cross-section, of the invention and is taken along the line 2-2 of FIG. 1.

FIG. 3 is a side elevational view of the right side of the apparatus shown in FIG. 1.

FIG. 4 is a side elevational view of the ratchet wheels associated with the pawl members shown principally in FIGS. 6, 7, and 8.

FIG. 5 is a side elevational view of the print head showing how it is connected to the guide bar means and the endless belt, and is taken along the line 55 of FIG. 1.

FIG. 6 is an enlarged plan View of a portion of FIG. 1 (with certain elements removed to simplify the drawing) showing a first operating lever in a first position, from which it is effective to prevent movement of the print head along the print line.

FIG. 7 is a plan view similar to FIG. 6 but showing the first operating lever in a second position, with one of the pawl members associated therewith in position to rotate a ratchet wheel to thereby index the print head.

FIG. 8 is a plan view similar to FIG. 6 showing a second operating lever means in position to permit the print head to be returned to the first print position.

FIG. 9 is a side elevational view of the means for rotating the guide bar means and is taken along the line 99 of FIG. 1.

FIG. 10 is a top plan view of FIG. 9.

FIG. 11 is a plan view of a thermal sensitive print medium which may be used with this invention.

FIG. 12 is a diagrammatic view, in block form, of a control circuit for the printer.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIGS. 1 and 2 show the general arrangement of elements in the printer 20 of this invention. The printer 20 includes a base 22, to which enveloping covers 24 and 26 (shown in dashed outline in FIG. 2) are pivotally joined. The cover 24 is joined to the base 22 by hinges 28 (one shown) and rotates clockwise (as viewed in FIG. 2) to expose the interior of the printer 20. The cover 26 is similarly joined to the base 22 by hinges 30 and rotates counter-clockwise (as viewed in FIG. 2) to expose the interior of the printer 20. The cover 24 has therein a slot 32, which is aligned parallel to the base 22 to permit the print medium 34 (shown in FIG. 11) to be fed therethrough. The adjacent edges of the covers 24 and 26 abut along the dashed line 36 when the covers are in the closed position shown in FIG. 2 except for a notched area 38, which is located in the cover 26. The print medium 34 passes out of the printer 20 through the notched area 38 after the printing operation is completed at the print line 40. A window 42 (FIG. 2), located in the cover 26, permits viewing of the print line 40 as the printing is effected.

The printing is effected by the print head 44, which is shown in FIGS. 1 and 5. The print head 44 is of the thermal matrix type, and, because the print head,

per se, does not form a part of this invention, it is shown only generally. Details of a print head which may be used in the printer 20 may be found in U.S. Patent No. 3,161,457, which issued Dec. 15, 1964, on the application of Hans Schroeder et al. and is assigned to the assignee of the present invention. Stated generally, the print head 44 includes thirty-five separate resistive elements which are arranged in a matrix of five columns of seven resistive elements per column. By selectively energizing the resistive elements with an electrical pulse of short duration, the selected resistive elements will experience a. rise in temperature of suflicient magnitude to produce a combination of dots in the form of the desired character on a thermally sensitive medium, like 34, in cooperative relationship with the print head 44. The thermally sensitive medium 34 may be of the commercially avialable type like NCR Thermal Copy Paper, manufactured by The National Cash Register Company, of Dayton, Ohio, United States of America.

The print head 44 is brought into cooperative engagement with the thermally sensitive print medium 34 by the following construction, which forms a part of this invention. The print head 44 is slidably mounted on a guide bar means which includes a guide bar 46, whose ends are pivotally mounted in bearings 48 (FIG. 2) for rotation between non-printing and printing positions relative to the print line 40. When the guide bar 46 is rotated to the non-printing position, shown in FIG. 5, the print head 44 is out of engagement with the print medium 34, and, when the guide bar 46 is rotated clockwise (as viewed in FIG. 5) by transport means to be described later, the print head is brought into engagement with the print medium 34. The bearings 48, which receive the ends of the guide bar 46, are positioned and fixed in vertical supports 50 and 52 (FIG. 1), so as to maintain the guide bar 46 parallel to the print line 40. Because the print head 44 is slidably mounted on the guide bar 46, it can be indexed along different print positions relative to the print line 40 by a conventional endless belt 54, which is a part of the transport means (to be described later) which rotates and indexes the print head. The endless belt 54 is a timing belt, which may be made of Dacron fibered urethane, and is secured to the print head by conventional brackets and screws 56, shown in FIGS. 1 and 5. The belt 54 is mounted on complementary pulleys 58 and 60. The pulley 58 (FIG. 2) is rotatably ,mounted on a post 62, which is positioned perpendicular to the base 22 and is fixed thereto. The pulley 60 (FIG. 4) is fixed to a shaft 64 to rotate therewith, and the shaft 64 is positioned perpendicular to the base 22 and is rotatably mounted therein.

The print head 44 is rotated into and out of engagement with the print medium 34 and is indexed along the print line 40 (FIG. 1) by transport means having the following construction. The transport means includes a first operating lever 66 having one end pivotally joined to the base 22 by a fastener 68, as is best shown in FIGS. 6, 7, and 8. The lever 66 is movable between first and second positions relative to the base 22 and is maintained in the first position (shown in FIG. 6) by a spring 70, which urges the lever 66 to rotate clockwise (as viewed in FIG. 6) about the fastener 68. The clockwise rotation of the lever 66 is limited by an adjustable stop 72, which is threadedly secured to a post 74, which is fixed to the base 22. A solenoid 76, having its operating plunger 78 pivotally joined to the lever 66 between its ends, is used to pivot the lever 66 to its second position, shown in FIG. 7. When the solenoid 76 is energized, the operating plunger 78 is pulled inwardly to pivot the lever 66 about the fastener 68 in a counter-clockwise direction as viewed in FIG. 7. Upon moving to the second position, the lever 66 is effective to rotate the print head 44 into engagement with the print medium 34.

The linkage operatively connecting the first operating lever 66 with the print head 44 to bring the print head into and out of engagement with the print medium 34 is shown principally in FIGS. 9 and 10. The linkage includes a link 80, having one end pivotally joined to the under side of the lever 66 and the other end thereof pivotally joined to one end of a lever 82. The link 80 is twisted between its ends, so that the ends lie in planes which are perpendicular to each other. The remaining end of the lever 82 is rotatably mounted on the guide bar 46. Another link 84 has one end pivotally joined to the lever 82 (by pin 86, FIG. 9) to be carried thereby. The remaining end of the link 84 is slotted to receive a pin 88, which is secured to one end of a lever 90. The remaining end of the lever is slotted to receive the guide bar 46 and is clamped thereto by a fastener 92. A spring 94 is used to urge the pin 88 towards the pin 86. The first operating lever 66 is shown in the first position in FIG. 9, and, when it is moved to the second position, the lower end of the lever 82 (as viewed in FIG. 9) is pulled by the link 80 to rotate the lever '82 about the guide bar 46 in a counterclockwise direction. As the lever 82 rotates counter-clockwise, the pin 86, carried thereby, pulls the spring 94, which in turn pulls the pin 86, which is secured to the lever 90, thereby resiliently rotating the lever 90 counter-clockwise. As the lever 90 is pulled counter-clockwise (as viewed in FIG. 9), the print head 44 (not shown in FIG. 9), mounted on the guide bar 46, is also rotated counterclockwise into engagement with the print medium 34. The force with which the print head 44 is held against the print medium is controlled by the spring 94. When the first operating lever 66 returns to the first position, the lever 82 is rotated clockwise about the guide bar 46, and the link 84 pushes the lever 90 in the same direction to move the print head 44 out of engagement with the print medium 34.

In addition to rotating the print head 44 into and out of engagement with the print medium 34, the transport means previously mentioned also includes means for indexing the print head 44 to successive print positions along the print line 40. The indexing means is best shown in FIGS. 3, 4, 6, 7, and 8 and includes the belt 54 and the pulleys 58 and 60 (FIG. 1) already generally described. The pulley 60 is fixed to rotate with the shaft 64, to which ratchet wheels 96 and 98 are also fixed. The wheel 96 lies above the wheel 98 (FIG. 6) and has its teeth 100 so arranged as to be driven clockwise (as viewed in FIG. 6) when pushed by the tfirst pawl member 102. The wheel 96 is prevented from rotating counter-clockwise whenever a third pawl member 104 engages a tooth 100, as shown in FIGS. 6 and 7. The ratchet wheel 98 has teeth 106, which are arranged thereon so as to prevent the clockwise rotation of the wheel 98 whenever a second pawl member 108 engages the teeth 106, as shown in FIGS. 6 and 8. The first pawl member 102 has one end pivotally joined to the operating lever 66 (FIGS. 6, 7, and 8) and has a spring secured to its other end, so as to urge the pawl member into engagement with the teeth 100 of the ratchet wheel 96. The third pawl member 104 has one end pivotally joined to a fastener 112, which is secured to the base 22, and its remaining end is urged into engagement with the teeth 100 of the ratchet wheel 96 by a spring 114, which is secured to the lever 66. The second pawl member 108 is pivotally mounted between its ends to a pin 116, which is carried by the lever 66, and one end of the pawl member 108 has a spring 118 secured thereto to urge its other end into engagement with the teeth 106 of the lower ratchet wheel 98. A pin 109, depending from the lever 66, keeps the second pawl member 108 from rotating when the pawl member disengages from the ratchet wheel 98.

The ratchet wheels 96 and 98, the pawl members 102, 104, and 108, and the first operating lever 66 cooperate to advance the print head 44 along the print line 40 as follows. When the first operating lever 66 is in the first position, shown in FIG. 6, the first pawl member 102 rests against a tooth 100 of the upper ratchet wheel 96; however, the second pawl member 108 engages a tooth 106 on the lower ratchet wheel 98 to prevent both wheels 96 and 98 from rotating clockwise, as viewed in FIG. 6, and the third pawl member 104 engages a tooth 100 on the upper ratchet wheel 96 to prevent both ratchet wheels 96 and 98 from rotating counter-clockwise. As pointed out earlier, both wheels 96 and 98 are fixed to the shaft 64. It should also be remembered that, when the first operating lever 66 is in the first position, shown in FIGS. 6 and 9, the link '80 (only a portion of which is shown in FIG. 6) maintains the guide bar 46 to the position shown in FIG. 9, from which position the print head 44 is held out of engagement with the print medium 34. Because the pulley 60 (FIG. 4) is fixed to the shaft 64, it is also locked against rotation in either direction when the operating lever 66 is in the first position, and consequently the belt 54, driven by the pulley 60, is also locked against movement. When the belt 54 is locked, the print head 44, which is moved along the guide bar 46 by the belt 54, is also locked against movement in either direction, to maintain column registration at the print line 40.

When the operating lever 66 is moved to the second position by energizing the solenoid 76, the following events occur. As previously mentioned, the link 80, attached to the lever 66, is effective to rotate the print head 44 into engagement with the print medium 34. As the lever 66 is pivoted (counter-clockwise, as viewed in FIG. 7) to the second position, the first pawl member 102 rides over one and a half teeth 100 of the first ratchet wheel 96 to the position shown. At the same time, the second pawl member 108 is pulled out of engagement with the teeth 106 of the second ratchet wheel 98, and the third pawl member 104 remains in engagement with the teeth 100 of the first ratchet wheel 96.

When the solenoid 76 is deenergized (after printing is effected), permitting the operating lever 66 to return to the first, or home, position, the following events occur. As the lever 66 rotates clockwise (as viewed in FIG. 7) by the urging of the spring 70, the link 80 begins to move the print head 44 away from engagement with the print medium 34, as previously explained. At this time, the first pawl member 102 has not as yet contacted a tooth 100 on the first ratchet wheel 96 to provide a delay which enables the print head 44 to be moved out of engagement with the print medium 34 before the print head 44 is indexed along the print line 40. This delay prevents smearing of the character printed due to the print head 44 being dragged across the print medium 34 while in contact therewith. By the time the print head 44 is moved out of engagement with the print medium 34, the first pawl member 102 (FIG. 7) engages a tooth 100 on the first ratchet wheel 96 and begins to rotate the first ratchet wheel 96 clockwise, as viewed in FIG. 7. While the first ratchet wheel 96 is being so rotated, the third pawl member 104 begins to ride over a tooth 100 on the wheel 96, and the second pawl member 108 begins to advance towards a tooth 106 on the second ratchet wheel 98. By the time the first pawl member 102 rotates the first ratchet wheel 96 an amount equivalent to one full tooth, the second pawl member 108 engages a tooth 106 on the second ratchet wheel 98 (as shown in FIG. 6) to prevent further clockwise rotation of the wheel 98, and the third pawl member 104 engages a tooth on the first ratchet wheel 96 to prevent counter-clockwise rotation of the wheel. This locking against rotation of the first and second ratchet wheels 96 and 98, respectively, enables the print head 44 to be kept in registration with the print positions along the print line 40 (FIG. 1). As previously explained, whenever the ratchet wheels 96 and 98 are rotated and locked, the pulley 60 is correspondingly rotated and locked to index the print head 44 (via the endless belt 54) along the guide bar 46.

The means for returning the print head 44 to the home position (that is, the left margin, as viewed in FIG. 1) is shown in FIGS. 1, 3, and 8. Whenever the print head 44 is to be returned to the home position before completing a full line of printing, the control circuit, shown only in general block form in FIG. 12, may be used to actuate the means for returning the print head to the home position. The print head 44 is also returned, automatically, to the home position upon completing a full line of printing as follows. When the print head 44 is indexed to the right (as viewed in FIG. 1) and approaches the right margin of the printing line, the print head 44 actuates a lever of a limit switch 122, which is secured to the support 52. When the switch 122 is closed, a circuit is completed to a solenoid 124 to energize it, and another circuit is completed to a return motor 126 to start it rotating. When the solenoid 124 is energized, its operating plunger 128 is pulled inwardly (FIG. 8), causing a second operating lever 130 (which is pivotally joined to the plunger 128 by a pin 132) to pivot about a fastener 134 in a clockwise direction, as viewed in FIG. 8. The plane of rotation of the lever 130 lies under the second ratchet wheel 98 (as viewed in FIG. 3), and consequently, when the lever 130 rotates clockwise, one end thereof engages a pin 136, de pending from the first pawl member 102, and a pin 138, depending from the third pawl member 104, to push these pawl members out of engagement with the first ratchet wheel 96. The remaining end (FIG. 3) of the second operating lever 130 has a portion 142 upstanding therefrom, and, when the solenoid 124 is energized, as previously explained, the end portion 140 also pivots about the fastener 134, relaxing the tension on a cable 144 (FIGS. 3 and 8). When the tension in the cable 144 is relaxed, a spring 146 pulls one end of a lever 148, causing the lever 148 to pivot about a pin 150 in a clockwise direction (as viewed in FIG. 3). When pivoting in said clockwise direction, the remaining end of the lever 148 moves away from a flange 151 on a clutch member 152, permitting a spring 154 to urge the clutch member 152 to the right (as viewed in FIG. 3) to move the face of the clutch member 152 into driving engagement with the face of a drive gear 156, causing it to be rotated by the motor 126. The drive gear 156 is rotatably supported and restrained against axial movement in a block 158 (FIG. 3), which is secured to the support 52, and the shaft (not shown) which rotatably supports the gear 156 is axially aligned with the drive shaft 160 of the motor 126. The motor 126 is supported on a block 162, which is also secured to the support 52. The clutch member 152 is keyed for rotation with the drive shaft 160 and is axially slidable thereon, and it has a plastic disc secured to its face to improve the driving connection between it and the drive gear 156. The drive gear 156 is in mesh with a gear 164 (FIG. 4), which is fixed to the shaft 64 to rotate it. When the motor 126 is energized, and the clutch member 152 is actuated as just explained, the pulley 60 (fixed to the shaft 64) is rotated counter-clockwise (as viewed in FIG. 1) to move the belt 54 in a direction which returns the print head 44 towards the first print position (or to the left, as viewed in FIG. 1). The print head 44 is advanced to the left by the motor 126 until it engages an operating arm 166 (FIG. 1) of a switch 168, which is secured to the support 50.

When the print head 44 engages the operating arm 166 (FIG. 1) of the switch 168 upon approaching the home position, the following events occur. The opening of the switch 168 is effective (through the control means shown in FIG. 12) to deenergize the motor 126 and the solenoid 124. After the motor 126 is deenergized, the print head 44 still retains some of its inertia in moving towards the left margin, and consequently it hits and rebounds from a resilient bumper 170, secured to the support 50. To maintain accurate registration of the print head 44 at the left margin, the print head 44 is kept from rebounding too far towards the right margin by the second pawl member 108 (FIG. 8), which engages a tooth 106 of the second ratchet wheel 98 to hold the print head at the left margin. When the solenoid 124 is deenergized, a spring (not shown) located in the solenoid 124 (FIG. 8) operates to push its associated plunger 128 outwardly, thereby pivoting the second operating lever 130 counterclockwise about the fastener 134, so as to permit the springs 110 and 114 to pull the pawl members 102 and 104, respectively, into engagement with the teeth 100 of the first ratchet wheel 96. As the second operating lever 130 pivots about the fastener 134 (counter-clockwise), it also pulls the cable 144 (to the right, as viewed in FIG. 3) to pivot the lever 148, pushing the clutch member 152 out of engagement with the face of the drive gear 156.

The feed means for advancing the print medium 34 past the print line 40 is shown principally in FIGS. 1 and 2. The feed means includes a pair of conventional spaced sprocket wheels 172 and 174, which are secured to a shaft 176, which is rotatably mounted in supports 178 and 180. These supports 178 and 180 are L shaped and are secured to the sides of vertical supports 182 and 184, respectively, which in turn are secured to the base 22. A paper guide, consisting of spaced parallel plates 186 and 190 (FIG. 2), is aligned with the slot 32 in the cover 24 to guide the print medium 34 towards the sprocket wheels 172 and 174. The plate 186 is secured to a block 188 (FIG. 2), and the upper plate 190 has downturned ends 192, which also are secured to the block 188. The sprocket wheels 172 and 174 have tines 194, which engage matching holes 196 in the print medium 34 (with copy 34a) shown in FIG. 11 to feed the print medium 34 past the print line 40 as the shaft 176 is rotated or indexed. The right-hand end of the shaft 176 (as viewed in FIG. 1) has a ratchet wheel 198 fixed thereto by a pin 200. The ratchet wheel 198 is prevented from rotating counterclockwise (as viewed in FIG. 3) by a leaf-type pawl 202, which is secured at one end to a block 204. The ratchet wheel 198 is indexed, one tooth 206 (FIG. 3) at a time, by a pawl 208, which is pivotally joined to one end of a lever 210 by a pin 212. The remaining end of the lever 210 is pivotally joined to the support 184 by a fastener 214, and the lever 210 is also pivotally joined between its ends to the plunger 216 of a solenoid 218 by a joining pin 220. When the solenoid 218 is energized, its plunger 216 is pulled inwardly, rotating the lever 210 about the fastener 214 in a counter-clockwise direction (as viewed in FIG. 3), causing the pawl 208 to rotate or index the ratchet wheel 198 (in a clockwise direction) one tooth position, which in turn rotates the sprocket wheels 172 and 174 an amount which is sufiicient to advance the print medium 34 to the next line of printing. The pawl 208 is urged into engagement with the teeth 206 of the ratchet wheel 198 by a spring 222, which is secured to a stop pin 224, which is fixed to the support 184. A second stop 226, also secured to the support 184, limits the extent of travel of the pawl 208 to one tooth on the ratchet wheel 198 for each energization of the solenoid 218. The plunger 216 is urged outwardly of the solenoid 218 to the position shown in FIG. 3 (when the solenoid is deenergized) by a spring (not shown) within the solenoid 218.

The control means for controlling the operation of the printer apparatus 20 may be conventional, as is shown in the United States patent to Meckstroth et al., previously mentioned, and, therefore, the control means for the apparatus 20 is shownonly diagrammatically in FIG. 12. During normal operation, when the print head 44 is to be returned to the home position before completing a full line of printing, the appropriate signal is received at the transducer logic 228, which sets up the print head return flip-flop 230 and the print head return one-shot 232. The print head one-shot 232 is used to turn off the return motor 126 and the solenoid 124 if the print head 44 fails to return to its home position within an allotted time which is approximately the time for printing two characters. The print head may be returned to the home position within the time for printing one character; however, to avoid high stresses generated in the linkage for returning the print head to the home position, a time for printing two characters was allotted for this function. A conventional driver 234 is utilized between the return flipflop 230 and the solenoid 124, and, similarly, a convenventional driver 236 is coupled between said flip-flop and the return motor 126. The return flip-flop 230 is reset normally by the opening of the switch 168 when the print head 44 engages the operating lever 166 of said switch upon approaching the left margin (FIG. 1). The switch 168 is positioned relative to the print line 40 so that it is opened when the print head 44 approaches the second print position from the left margin, and the switch 168 remains open while the print head 44 is at the first print position, or left margin. While the print head remains at the first print position, the solenoid 218 may be repeatedly energized via a line feed one-shot 238 and driver 240 (FIG. 12) for repeated linefeed instructions, but the return flip-flop 230 will be held in the reset position by the open switch 168. In the embodiment shown herein, the one-shot 232 is timed for approximately milliseconds to allow the print head 44 to be readied for the next advance instruction. The advance instructions are routed through the advance one-shot 242 and the driver 244 to the solenoid 76. After approaching the second print position, the movement of the print head 44 permits the switch 168 to be closed. When the print head 44 advances to the extreme right of the print line 40, the switch 122 will be closed to energize the return one-shot 232, causing the print head 44 to be returned automatically to the first print position, as previously explained.

Some additional miscellaneous details of the printer mechanism 20 are as follows. The print head 44 (FIG. 1) has one end of a multiple conductor cable 246 connected thereto, with the remaining ends of the cable being connected to a terminal block 248. The terminal block 248 is connected to individual posts on a connector 250, which is used to interface the printer with an external control device such as a computer or a keyboard (not shown). The individual solenoids 76, 124, and 218 and the motor 126 consume small amounts of electricalpower,

making the printer adaptable for battery operation. The

size of the printer 20 in its illustrated embodiment is approximately seven inches wide, seven inches long, and two and three quarter inches high.

What is claimed is:

1. A printer apparatus comprising: v

frame means having a print line located therein, with said'print line having a plurality of print positions therealong; I

a guide bar means pivotally mounted in said frame means for movement between non-printing and printing positions relative to .said print line;

a print head slidably mounted on said guide bar means for movement along said print line between the first and'last of said print positions;

and transport means for rotating said guide bar mean from said non-printing position to said printing position, thereby moving said print head into engagement with a print medium positioned at said print line to effect printing thereon, and for rotating said guide bar means from said printing position to said non-printing position, thereby moving said print head out of engagement with said print medium and thereafter moving said print head one print position towards said last print position;

said transport means comprising:

ratchet wheel means rotatably mounted in said frame means;

an endless belt operatively connected to said ratchet wheel means to be moved thereby upon the rotation of said ratchet wheel means, said print head being secured to said belt to be moved thereby along said print line;

operating lever means movable between first and second positions in said frame means;

pawl means associated with said ratchet wheel means to prevent the rotation thereof while said lever means is in said first position; and

connecting lever means operatively connecting said operating lever means with said guide bar means so as to rotate said guide bar means to said printing position when said operating lever means is moved to said second position, and to return said guide bar means to said non-printing position as said connecting lever means is moved to said first position, said pawl means being effective to rotate said ratchet wheel means after said print head is moved out of engagement with said print medium by said guide bar means but before said operating lever means reaches said first position so as to thereby move said print head one print position towards said last print position.

2. The apparatus as claimed in claim 1 in which said print head is of the thermal matrix type, and said print medium is thermally sensitive.

3. The apparatus as claimed in claim 2 further comprising return means for returning said print head to said first print position after printing at said last print station.

4. The apparatus as claimed in claim 2 in which said ratchet wheel means includes first and second ratchet wheels rotatably mounted in said frame means and fixed to rotate together; and in which said pawl means include first and second pawl members pivotally mounted on said connecting lever means, and a third pawl member pivotally mounted on said frame means; said first pawl member being adapted to engage the teeth of said first ratchet wheel and rotate said ratchet wheels in a first direction which moves said print head towards said last print position when said operating lever means is moved towards its said first position from said second position, said second pawl member being adapted to engage the teeth of said second ratchet wheel as said operating lever means moves to said first position so as to permit only that angular rotation of said first ratchet wheel which corresponds to a print head movement of one print position towards said last print position; said third pawl member being adapted to engage the teeth of said second ratchet wheel to permit only a rotation of said first ratchet wheel in 10 said first direction while engaging said second ratchet wheel.

5. The apparatus as claimed in claim 4 further including return means for returning said print head to said first position, comprising:

second operating lever means movable between first and second positions in said frame means, and being out of engagement with said first and third pawl members when in said first position and being in engagement therewith when in said second position to move said first and third pawl members out of engagement with said first ratchet wheel;

and actuator means for rotating said ratchet wheel means in a direction which moves said print head to said-first of said print positions when said second lever means is in said second position;

said second pawl means being adapted to engage the teeth of said second ratchet wheel so as to prevent rebounding of said print head away from said first print position when returned thereto.

6. The apparatus as claimed in claim 5 in which:

said actuator means includes a motor operatively connected to said ratchet wheel means and said endless belt;

said first-named operating lever means includes a first actuator for moving it from said first position to said second position, and means for returning said first-named operating lever means to said first position;

and said second operating lever means includes a second actuator for moving it from said first position to said second position, and spring means for returning said second lever means to said first position.

7. The apparatus as claimed in claim 6 in which said apparatus also includes feed means for moving said print medium transversely across said print line, said motor and first and second actuators being electrically operated.

References Cited UNITED STATES PATENTS 2,851,141 9/1958 Kistner 197-1 2,911,085 11/1959 Leathers 197-1 3,139,026 6/1964 Meckstroth 197-1 XR 3,198,306 8/1965 Bachman 197-1 3,236,351 2/1966 Fitch et a1 197-1 3,292,530 12/1966 Martin 1971 XR 3,300,017 1/1967 Yazejian et al. 197-1 3,353,648 11/1967 Sanae Amada et al. 197-55 3,354,817 11/1967 Sakurai et al. 197-1 XR 3,378,127 4/1968 Clary et al. 197-55 3,426,880 2/1969 Blodgett l971 EDGAR S. BURR, Primary Examiner US. Cl. X.R. 197-55; 346-74, 46 

